Download and install the ZiPhone double clicking and extracting the folder on your desktop to start the process of changing the IMEI.
Open the program command "Run" and type "cmd" without the quotes. This option will find it by clicking "Start> Run".
Type cd Desktop / ZiPhone in the search field and press "Enter" on your computer. Connect your iPhone to your computer using the cable from iPhone.
Put the iPhone in restore mode. Press the "On" and "Off / On" ("Sleep / Wake") simultaneously until you see the Apple logo buttons; then release the "Power" button. Continue pressing the "Off / On" button until you see the iTunes logo and cable on your screen.
To complete the process of changing the IMEI of your iPhone type "u ia Ziphone 123456789012345" in the command prompt. Change IMEI numbers you want to change.
Wait for the program to locate the file zibri.dat. Your iPhone 4 will restart automatically and you will be the new IMEI on your iPhone.